MCAO for the European Solar Telescope: first results

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1 MCAO for the European Solar Telescope: first results Marco Stangalini Roberto Piazzesi Dario Del Moro Francesco Berrilli Alberto Egidi Università di Roma Tor Vergata

2 EST EST is a pan-european project, presently in its Conceptual Design Study financed by the European Commission It will be a 4-meter class solar telescope, to be located in the Canary Islands It will be optimised for studies of the magnetic coupling between the deep photosphere and upper chromosphere multiple wavelength imaging 2D spectroscopy and spectropolarimetry high temporal resolution high spatial resolution Marco Stangalini EST-MCAO 2

3 swp5300 led by UToV, provides the heat rejector /stop design in compliance with telescope optical design UtoV partecipates in WP6000 Wavefront reconstruction for the MCAO system Marco Stangalini EST-MCAO 3

4 EST MCAO REQUIREMENTS 1' corrected FoV MCAO system High servo loop stability High order correction (300 th -400 th aberration order) High efficiency wavefront reconstruction Marco Stangalini EST-MCAO 4

5 EST MCAO DIFFICULTIES Daytime turbulence High speed wavefront analisys (less than 1 ms) Low contrast target Time delay error Mirror seeing Need for detailed performance studies through simulations and tests Marco Stangalini EST-MCAO 5

6 Layer Oriented MCAO We have investigated the layer oriented approach with a 7 points exagonal asterism 6

7 MCAO simulations Layer Oriented approach (Ragazzoni R. et al 2002): FFT turbulence layers with WFS fine tuning 7 wavefront sensors LOST simulation tool (Arcidiacono, C. et al. 2004) Solar Package plugin to fit solar case needs: WFS noise treatment for extended sources Time delay reduction with turbulence forecasting Marco Stangalini EST-MCAO 7

8 Simulation setup Working wavelength: 555 nm 2 DMs Conjugation altitudes: 0 Km, 10 Km Integration times + loop delay: 1.5 ms 30x30 WFS sampling 2 Kolmogorov turbulence layers (FFT): 0 km, 10 km D/r0 : 26, 8 Marco Stangalini EST-MCAO 8

9 Strehl ratio maps radius radius radius (SR = PSF peak / diffraction limited PSF) Marco Stangalini EST-MCAO 9

10 Modal approach We have tested a modal approach for wavefront reconstruction The best results in terms of SR peak and sky coverage are achieved with a 300 th order base dimension Finite sampling effects on modal reconstruction (30 x 30 WFS subapertures) Marco Stangalini EST-MCAO 10

11 Time delay error In order to reduce time delay effects we propose the use of some prediction tools: Modal coefficients forecasting with ARMA stationary processes Modal coefficients forecasting with linear predictor algorithm Marco Stangalini EST-MCAO 11

12 Forecasting SR With linear prediction SR Without linear prediction Marco Stangalini EST-MCAO 12

13 Modal optimization We have studied modal base optimization using information theory on VTT (Vacuum Tower Telescope) real WFS data Mutual information reordering lets us shrink the base dimension while keeping the reconstruction error fixed Marco Stangalini EST-MCAO 13

14 To be done... New neural network learning algorithm for the Linear Predictor Mirror seeing treatment Shell models turbulence simulations Testing ARMA forecasting in closed loop conditions References: Arcidiacono, C., Diolaiti, E., Tordi, M., Ragazzoni, R., Farinato, J., Vernet, E., & Marchetti, E Layer-oriented simulation tool. Applied optics, 43(22), Ragazzoni, R., Diolaiti, E., Farinato, J., Fedrigo, E., Marchetti, E., Tordi, M., & Kirkman, D Multiple field of view layer-oriented adaptive optics. A&A, 396, EST-SRD, EST Scientific Board (Dec.). Science Requirements document for EST v6d2. SRD. Marco Stangalini EST-MCAO 14

15 ARMA forecasting Zernike forecasting using ARMA(2,3) process on real VTT (Vacuum Tower Telescope) WFS data Coefficient prediction could play an important role in time delay reduction in the loop closure of AO sistems Marco Stangalini EST-MCAO 15